Gas turbine engines typically include a rotor assembly, a compressor, and a turbine. The rotor assembly includes a fan that has an array of fan blades extending radially outward from a rotor shaft. The rotor shaft transfers power and rotary motion from the turbine to both the compressor and the fan and is supported longitudinally using a plurality of bearing assemblies. Additionally, the rotor assembly has an axis of rotation that passes through a rotor center of gravity. Known bearing assemblies include rolling elements and a paired race, wherein the rolling elements are supported within the paired race. To maintain a rotor critical speed margin, the rotor assembly is typically supported on three bearing assemblies, one of which is a thrust bearing assembly and two of which are roller bearing assemblies. The thrust bearing assembly supports the rotor shaft and minimizes axial and radial movement of the rotor shaft assembly. The remaining roller bearing assemblies support radial movement of the rotor shaft.
During operation of the engine, a fragment of a fan blade may become separated from the remainder of the blade. Accordingly, a substantial unbalanced rotary load may be created within the damaged fan and must be carried substantially by the fan shaft bearings, the fan bearing supports, and the fan support frames.
To minimize the effects of potentially damaging abnormal unbalanced loads, known gas turbine engines include support components for the fan rotor support system that are sized to provide additional strength. However, increasing the strength of the support components undesirably increases an overall weight of the engine and decreases an overall efficiency of the engine when the engine is operated without substantial rotor imbalances.
Other known engines include a bearing support that includes a mechanically weakened section, or primary fuse, that decouples the fan rotor from the fan support system. During such events, the fan shaft seeks a new center of rotation that approximates that of its unbalanced center for gravity. This fuse section, in combination with a rotor clearance allowance, is referred to as a load reduction device, or LRD. The LRD reduces the rotating dynamic loads in the fan support system.
After the primary fuse fails, the pitching fan rotor often induces a large moment to the next closest bearing. In many configurations, the next closest bearing is known as the number two bearing position. The moment induced to the number two bearing induces high bending and shear loads to the fan rotor locally. To relieve the high shear stresses, the radial stiffness of the number two bearing position is often softened or reduced. However, to accommodate the axial loading transmitted through the engine, the number two bearing support must also provide high axial stiffness.
Current bearing assemblies are available that provide for a softened radial stiffness while still providing substantially high axial stiffness. However, as the bypass ration and thermal efficiency of modern gas turbine engines are increased, the resulting axial and radial loads transmitted through such engines correspondingly increase. Thus, current bearing assemblies must be redesigned to accommodate such increased turbine loads.
Accordingly, a bearing assembly that provides improved radial stiffness and/or axial stiffness to assist in accommodating the increased radial and/or axial loads of modern gas turbine engines would be welcomed in the technology.